ref: d7f37646965ee26214da0e1d97f3c1d54349ae2d
dir: /testdir/t.delete2/
NR < 50 { n = split($0, x)
for (i = 1; i <= n; i++)
for (j = 1; j <= n; j++)
y[i,j] = n * i + j
for (i = 1; i <= n; i++)
delete y[i,i]
k = 0
for (i in y)
k++
if (k != int(n^2-n))
printf "delete2 miscount %d vs %d at %d\n", k, n^2-n, NR
}